Portable gas torch

ABSTRACT

A portable gas torch has a metal burner tube defining a gas flow passage through which gas is adapted to flow. An igniter wire in the gas flow passage generates a spark to ignite gas flowing through the passage. The torch has a wire holder for positioning the igniter wire in the gas flow passage and a flame holder downstream from the wire holder. The wire holder comprises a central hub having an axial bore and at least one spacer on the hub for contacting an inside wall of the burner tube to position the hub at a predetermined radial location in the gas flow passage. The axial bore is sized to enable the wire to be held at a selected location downstream from the hub. The wire holder comprises a dielectric material to allow a spark to jump to the inside wall of the burner tube.

BACKGROUND OF THE INVENTION

[0001] The present invention relates generally to a portable gas torch,and more particularly to a portable gas torch having a wire holder forpositioning an igniter wire in the torch.

[0002] A typical self-lighting portable gas torch has a trigger actuatedpiezoelectric igniter system electrically connected to an igniter wireextending into a burner tube of the torch. The igniter system generatesa spark between the end of the igniter wire and the metal burner tube toignite a mixture of air and fuel flowing through the tube. A flameholder in the burner tube creates turbulent flow of the air-fuel mixtureso that the full diameter of the flowing gas stream is ignited toproduce a uniform flame for heating, brazing, or soldering.

[0003] To insure reliable flame ignition, the spark-emitting end of theigniter wire is positioned approximately {fraction (1/4)}″ upstream ofthe flame holder to provide a ⅛″ spark perpendicular to the gas flowthrough the burner tube. In typical igniter systems, the position of theigniter wire is maintained by lightly clamping an electrical forkedspade terminal to the igniter wire or by using a thin-formed sheet metalwire holder in the tube. Electrical spade terminals and sheet metal wireholders are typically made of metal for strength and are configured tominimize flow restriction. To prevent short-circuiting the spark, thewire end must extend significantly beyond the conductive metal wireholder necessitating frequent visual inspection and adjustment of thewire position to insure the correct spark gap is maintained. Because theflame holder prevents access to the wire end, a threaded removable brassburner tube is typically used to allow access to the igniter wire.

[0004] In order to produce a full flame downstream of the flame holder,the air-fuel mixture flow rate must be properly adjusted and an adequatefuel supply must be present. Frequently, operator error or use of a nearempty fuel cylinder results in a condition in which the air-fuel mixtureflow rate is insufficient to properly ignite the torch flame. When theigniter system is actuated during low-flow operation, the resultingflame will encompass the full flowing diameter of the air-fuel mixtureupstream of the flame holder causing rapid heating of the wire holder,wire, flame holder, and burner tube. Existing portable torch designswith conductive metal wire holders and removable brass tips prematurelyfail as a result of the rapid overheating that occurs during thelow-flow burn in the torch.

SUMMARY OF THE INVENTION

[0005] Among the several objects of this invention may be noted theprovision of a portable gas torch with an igniter wire holder which isrelatively economical to manufacture; the provision of such a torchwhich is easy to assemble with the igniter wire of the torch properlypositioned in the burner tube; the provision of such a torch whichreduces maintenance; the provision of such a torch which is durable; theprovision of such a torch which facilitates flame ignition duringlow-flow operation; and the provision of such a torch which allowsreliable spark gap control.

[0006] In general, a portable gas torch of the present inventioncomprises a metal burner tube defining a gas flow passage through whichgas is adapted to flow along a longitudinal axis of the tube to anoutlet. An igniter wire in the gas flow passage has a spark end forgenerating a spark to ignite gas flowing through the passage. The torchhas a wire holder for positioning the igniter wire in the gas flowpassage and a flame holder in the gas flow passage downstream from thewire holder. The wire holder comprises a central hub having an axialbore generally parallel to the longitudinal axis of the burner tube andat least one spacer on the hub for contacting an inside wall of theburner tube to position the hub at a predetermined radial location inthe gas flow passage. The axial bore is sized to enable the spark end ofthe wire to be inserted through the bore and then held at a selectedlocation downstream from the hub. The wire holder comprises a dielectricmaterial whereby a spark from the spark end of the igniter wire willjump to the inside wall of the burner tube even if the spark end ispositioned closer to wire holder than to the inside wall of the tube.

[0007] In another aspect of the invention, a portable gas torchcomprises a burner tube defining a gas flow passage through which gas isadapted to flow along a longitudinal axis of the tube, the tube havingan open end defining an outlet of the torch. An igniter wire in the gasflow passage has a spark end for generating a spark to ignite gasflowing through the passage. The torch has a dielectric wire holder inthe burner tube for receiving the igniter wire and positioning the sparkend in the gas flow passage and a flame holder in the gas flow passagedownstream from the wire holder. The wire holder comprises a central hubhaving an axial bore generally parallel to the longitudinal axis of theburner tube and a plurality of spacers extending from the hub forcontacting an inside wall of the burner tube to position the hub at apredetermined radial position in the gas flow passage. The axial bore issized to hold the igniter wire in place by an interference fit such thatthe spark end of the igniter wire is held a substantially fixed distancedownstream from the hub whereby a spark from the spark end of theigniter wire will jump to the inside wall of the burner tube even if thespark end is positioned closer to wire holder than to the inside wall ofthe tube.

[0008] Other objects and features will be in part apparent and in partpointed out hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]FIG. 1 is a perspective of one embodiment of a portable gas torchof the present invention.

[0010]FIG. 2 is a section of a tip assembly of the cutting torch.

[0011]FIG. 2A is an enlarged portion of FIG. 2 showing the connection ofthe tip assembly to a handle of the torch.

[0012]FIG. 3 is an enlarged portion of FIG. 2 showing a wire holder andflame holder of the torch.

[0013]FIG. 4 is a perspective of the wire holder of the torch.

[0014]FIG. 5 is a cross-section taken along the plane including line 5-5of FIG. 4.

[0015]FIG. 6 is a cross-section taken along the plane including line 6-6of FIG. 4.

[0016]FIG. 7 is a perspective of a second embodiment of the wire holder.

[0017]FIG. 8 is a cross section taken along the plane including line 8-8of FIG. 7.

[0018]FIG. 9 is a perspective of a third embodiment of the wire holder.

[0019] Corresponding parts are designated by corresponding referencenumbers throughout the drawings.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0020] Referring now to the drawings, and more particularly to FIG. 1,one embodiment of a portable gas torch of the present invention isdesignated in its entirety by the reference numeral 1. The torch 1 has ahandle 3 for connection to a fuel supply tank (not shown), aconventional trigger actuated piezoelectric igniter, generallydesignated 5, for creating a spark to ignite a flame in the torch, and atip assembly, generally designated 7, threadably attached to the handlehaving a metal burner tube 11 defining an outlet 13 of the torch. Thetorch 1 is configured so that a mixture of air and fuel flowing throughthe burner tube 11 is ignited by actuating the piezoelectric igniter 5so that a flame is emitted from the outlet 13 of the torch. The torch 1is particularly useful in providing a portable flame that can be used inheating, soldering, or brazing various components.

[0021] As shown in FIGS. 1-3, the handle 3 houses a lead wire 17electrically connected at one end to the piezoelectric igniter 5 and atits other end to an igniter wire 19 in the tip assembly 7 so thatcurrent generated in the piezoelectric igniter is conducted through theigniter wire. The igniter wire 19 may be, for example, a flexible wirecomprising one or more conductive elements in a flexible sheath ofdielectric material. As shown in FIG. 2A, the tip assembly 7 includes atip nut 23 that threadably attaches the burner tube 11 to the handle 3.An insulator 25 is received in the tip nut 23 and has an angled bore 27that receives a proximal end 29 of the igniter wire 19. A conductivering 31 is held in place around the insulator 25 to electrically connectthe igniter wire 19 with the lead wire 17 connected to the piezoelectricigniter 5. The igniter wire 19 is substantially insulated except for itsproximal end 29 in contact with the conductive ring 31 and its spark end33 held in the burner tube 11. Current generated by triggering thepiezoelectric igniter 5 travels through the lead wire 17, the conductivering 31, and the igniter wire 19 to generate a spark at the spark end 33of the igniter wire as will be described in more detail below.

[0022] Referring to FIG. 2, the burner tube 11 of the illustratedembodiment is a stainless steel tube with a cylindrical wall having aninner surface 41 defining a flow path for mixed air and fuel to passthrough the torch 1 to an open end forming the outlet 13 of the torch.It will be understood that the tube 11 can be comprised of othersuitable metals (i.e., other steels) or other electrically conductivematerials. The tube 11 has straight inlet section 45 extending from thehandle 3 of the torch 1, a bent intermediate section 49, and a straightoutlet section 53 having a longitudinal axis 55. In the illustratedembodiment, the outlet section 53 is bent approximately 60 degrees withrespect to the inlet section 45, but it will be understood that the tube11 could have other configurations including straight. As shown in FIG.2, the burner tube 11 is constructed from a single piece of metal tubingand has a substantially uniform flow diameter through its inlet section45, intermediate section 49, and outlet section 53. The inlet section 45of the tube 11 has a telescoping fit with a mixer 57 mounted on thehandle 3 of the torch for the flow of mixed air and fuel into the tube.

[0023] As shown in FIG. 2, the igniter wire 19 is disposed in the tipassembly 7 with the spark end 33 of the igniter wire held in a fixedradial and longitudinal position in the burner tube 11 by a wire holder61 received in the outlet section 53 of the tube. As seen in FIG. 2A,the proximal end 29 of the igniter wire 19 is received in the angledbore 27 in the insulator 25 and secured to the handle 3 of the torch 1by the retaining nut 23 which, when tightened on the handle, forces theproximal end of the igniter wire into electrical contact with theconductive ring 31. In the embodiment of FIG. 2, the igniter wire 19 isrouted from the angled bore 27 in the insulator 25 through the inletsection 45 of the burner tube 11 where the igniter wire is held againstthe inner surface 41 of the tube. The igniter wire 19 is spaced awayfrom the inner surface 41 of the intermediate section 49 of the tube 11and extends into the outlet section 53 of the tube where the igniterwire is held in the wire holder 61 approximately along the central axis55 of the tube. A spiral flame holder 65 is received in the outletsection 53 of the tube 11 between the spark end 33 of the igniter wire19 and the outlet 13 of the tube to turbulate the flow of gas downstreamfrom the flame holder. As shown in FIG. 3, the flame holder 65 is fixedin the tube 11 by engagement with a reduced-diameter annular section 69of the outlet section 53 of the tube. The flame holder 65 is held in thedesired position in the burner tube by an interference fit with thereduced-diameter annular section 69. Typically, the flame holder 65 ismade from metal (e.g., steel or brass) to withstand the high operatingtemperatures of the torch 1.

[0024] Referring to FIGS. 3-6, one embodiment of the wire holder 61 ofthe present invention comprises a solid cylindrical central hub 81having a central bore 83 generally parallel to the longitudinal axis 55of the outlet section 53 of the burner tube 11. As shown in FIGS. 4 and5, the central hub 81 has a flat upstream end surface 89 with a roundedperipheral edge 91, a substantially planar downstream end surface 99,and diametrically opposed arcuate side surfaces 95 extending axiallybetween the end surfaces 89, 99. The axial bore 83 of the hub 81 issized to enable the spark end 33 of the igniter wire 19 to be insertedthrough the bore to a position in which the spark end of the wire isheld at a fixed radial and longitudinal location downstream from the huba distance D (FIG. 3). The axial bore 83 has a converging inlet section103 and a downstream section 105 of uniform diameter. By having aninitial diameter approximately equal to the diameter of the igniter wire19, the inlet section 103 of the bore 83 is configured to facilitateinsertion of the igniter wire through the hub 81. The uniform diameterof the downstream section 105 is sized slightly smaller than thediameter of the igniter wire 19 for gripping the wire and holding it ina selected position by an interference fit. The friction fit between theigniter wire 19 and the hub 81 also holds the hub at a fixedlongitudinal location in the burner tube 11. By way of example and notlimitation, the inlet section 103 of the bore 83 may have an initialdiameter ranging from approximately 0.04 to 0.08 inches; the downstreamsection 105 may have a diameter ranging from approximately 0.02 to 0.07inches; and the insulated igniter wire 19 may have an outer diameterranging from approximately 0.05 to 0.09 inches. In one particularembodiment, the inlet section 103 has an initial diameter of about 0.06inches, the downstream section 105 has a diameter of about 0.04 inches;and the insulated igniter wire 19 has an outer diameter of about 0.05inches.

[0025] The wire holder 61 further comprises at least one spacer 109 onthe hub 81 for positioning the hub at a predetermined radial position inthe gas flow passage of the torch 1. In the particular embodiment ofFIGS. 2-6, two spacers 109 resembling arms extend radially from oppositesides of the hub 81 and contact the inside wall 41 of the burner tube 11so that the wire holder 61 is held in a predetermined radial positioninside the tube, e.g., a position where the central axis of the hub issubstantially coincident with the longitudinal axis 55 of the outletsection 53 of the burner tube. As shown in FIGS. 4 and 6, each spacer109 comprises an elongate solid body 115 integrally formed with the hub81 with the second spacer located approximately 180 degrees from thefirst spacer. In the embodiment of FIGS. 4-6, the spacer body 115 has arounded upstream end surface 123, a generally planar downstream endsurface 127, and two generally parallel side faces 119 extending axiallybetween the end surfaces 123, 127. The downstream end surface 127 isgenerally coplanar with the downstream end surface 99 of the hub 81 andperpendicular to the longitudinal axis 55 of the outlet section 53 ofthe burner tube 11. The rounded upstream end surfaces 89 and 123 of thehub 81 and the spacers 109 limit the flow disturbance created by thewire holder 61 in the flow path of the air-fuel mixture flowing throughthe burner tube 11. In one embodiment, the spacers 109 have free outerends 131 with rounded corners 135 for contact with the inner surface 41of the burner tube 11. It will be understood that one spacer or morethan two spacers can be provided for contacting the burner tube 11 andfixing the wire holder 61 in a predetermined radial position in thetube. Also, the wire holder 61 may have spacers 109 with configurationsother than those shown in the illustrated embodiments without deviatingfrom the scope of this invention.

[0026] By way of example but not limitation, the overall length of thewire holder 61 may be sized for a slip fit in the burner tube 11 with atotal preferred clearance of about 0.004 inches to about 0.008 inchesbetween each free end 131 of the wire holder and the inside wall 41 ofthe burner tube. In one embodiment, a typical overall length betweenopposed free ends 131 of the wire holder 61 may be approximately 0.430inches and a typical inside diameter of the burner tube may beapproximately 0.442 inches. It will be understood that the wire holder61 may be held in the hub 81 at a predetermined radial position in thetube 11 by other dimensional fits (i.e., press fit or interference fit)or by other attachment methods (i.e., adhesives or thermal bonding). Thewire holder 61 in the embodiment of FIGS. 2-6 is a single molded partmade of ceramic material but it will be understood that the wire holdercan be made from other dielectric materials (i.e., thermoplastics,composites, etc.) having suitable strength characteristics andtemperature resistance.

[0027] The dielectric wire holder 61 of the present invention allows aspark from the spark end 33 of the igniter wire 19 to jump to the insidewall 41 of the burner tube 11 even if the spark end is positioned closerto the wire holder than to the inside wall of the tube. As seen in FIGS.2 and 3, the insulated igniter wire 19 is received in the axial bore 83of the wire holder 61 and held in a fixed radial position in the burnertube 11 by the interference fit with the wall defining the downstreamsection 105 of the axial bore of the wire holder. As seen in FIG. 3, theexposed spark end 33 of the igniter wire 19 extends past the flatdownstream end surface 99 of the wire holder hub 81 a distance D so thatcurrent in the igniter wire can generate a spark from the exposed end ofthe wire to the inner surface 41 of the metal burner tube 11.

[0028] In prior designs involving metallic wire holders, it wasnecessary to extend the igniter wire a relatively large distance beyondthe wire holder to prevent short circuiting of the spark to the wireholder. Due to the relatively long unsupported length of flexible wire,a consistent spark gap between the spark end of the wire and the burnertube was difficult to maintain, and frequent manual adjustment duringassembly and operation of the torch was often required. This adjustmentwas facilitated by making the tip of the burner tube removable. In thedesign of the present invention, the distance D can be made relativelyshort, since the wire holder 61 is of a dielectric material and the riskof a short circuit of the spark to the wire holder is eliminated.Because distance D is short, the radial location of the spark end 33 ofthe wire 19 remains substantially fixed during torch assembly andoperation so that a more consistent spark gap is maintained. As aresult, the need for frequent positioning adjustments of the spark end33 of the wire 19 is eliminated and the burner tube 11 can be made of asingle piece rather than multiple pieces for reduced cost.

[0029] By way of example but not limitation, the distance D may be about0.01 inches to about 0.08 inches and more preferably from about 0.03inches to about 0.06 inches. In the illustrated embodiment, the sparkend 33 of the igniter wire 19 is located approximately on the centerlongitudinal axis 55 of the outlet section 53 of the burner tube 11, butit will be understood that the spark end can be otherwise located in theburner tube without departing from the scope of this invention.Preferably, the spark end 33 of the igniter wire 19 is spaced from theinner surface 41 of the burner tube 11 by about 1 mm to about 6 mm andmore preferably about 3 mm to about 4 mm. Also, the spark end 33 of theigniter wire 19 is preferably spaced a distance of approximately{fraction (1/4)}″ upstream of the flame holder 65 to facilitate properflame ignition of the torch 1.

[0030] In normal operation, the torch 1 is first properly adjusted sothat the air-fuel mixture flows through the burner tube 11 at asufficient rate to generate a useable flame extending from the outlet 13of the torch. After setting the air-fuel mixture flow rate, thepiezoelectric igniter 5 is actuated to produce an electrical currentflowing through the igniter wire 19 in the tip assembly 7. Theelectrical current in the igniter wire 19 results in a spark which jumpsin a direction substantially perpendicular to the flow of gas throughthe tube from the exposed end 33 of the igniter wire held in the wireholder 61 to the inner surface 41 of the burner tube 11. The sparkignites a small flame kernel in the air-fuel mixture flowing past thewire holder 61. The flame kernel passes through the flame holder 65which fully turbulates the air-fuel mixture causing the full flowdiameter of the mixture to ignite downstream of the flame holder. Theresulting flame exits the outlet 13 of the burner tube so that the torch1 emits a fully ignited flame that is suitable for many uses includingheating, brazing, soldering, or similar processes.

[0031] In an upset condition in which the flow settings of the torch 1are incorrectly set or the fuel supply is low, the amount of air-fuelmixture flowing through the burner tube 11 will be insufficient toproduce a full flowing flame extending from the outlet 13 of the torch.In this low flow condition, the spark between the igniter wire 19 andthe inner surface 41 of the burner tube 11 will prematurely ignite thefull flow diameter of the mixture to create a flame upstream of theflame holder 65. The flame created during this low-flow condition willnot propagate through the outlet 13 of the burner tube 11 in an amountsufficient to be a useable flame. The premature ignition of the flame atthe low-flow condition results in rapid overheating of the wire holder61, igniter wire 19, flame holder 65 and burner tube 11. The wire holder61 of the present invention is designed to minimize flow restriction inthe burner tube 11, thus lowering the flow setting at which prematureflame ignition occurs. Also, the flat downstream surfaces 99 and 127 ofthe wire holder 61 causes the flame to burn far enough downstream of thewire holder to reduce the heat transferred to the wire holder and theigniter wire 19. The configuration of the present invention with aceramic wire holder 61 and a stainless steel burner tube 11 canwithstand extreme abuse and high temperatures during low-flow operationto allow the portable torch 1 to function properly after proper flowthrough the torch has been restored.

[0032] A second embodiment of a wire holder of the present invention,generally designated 201, is shown in FIGS. 7 and 8. The wire holder 201of this embodiment is a single molded part made from a high-temperaturethermoplastic (e.g., alumina) and molded to have generally an airfoilshape. The wire holder 201 has a central hub 205 and two aligned radialspacers 209 formed integrally with the hub. The spacers 209 terminate inouter (free) ends 213 that contact the inner surface 41 of the burnertube 11 to fix the wire holder 201 at a predetermined radial position inthe tube. As shown in FIG. 8, the hub 205 has an axial bore 217 with anupstream section 221 of converging diameter, a short intermediatesection 225 of uniform diameter, and a downstream section 229 ofdiverging diameter. The hub 205 of this embodiment 201 allows insertionof the igniter wire 19 from either the upstream end or the downstreamend of the axial bore 217. The intermediate section 225 of the bore 217is sized for interference fit with the igniter wire 19 so that theposition of the igniter wire is substantially fixed upon insertion intoand through the wire holder 201. Each of the spacers 209 has an airfoilshape with opposed curved axially-extending faces 233 that converge atnarrow upstream edges 237 and downstream edges 241. The airfoil shape ofthe wire holder 201 minimizes the flow disturbance in the burner tube 11to reduce the flow rate at which premature flame ignition occurs duringlow-flow operation.

[0033] A third embodiment of a wire holder of the present invention,generally designated 301, is show in FIG. 9. This embodiment 301 issubstantially similar to the second embodiment 201 except that the wireholder has three spacers 305 extending radially from the hub 309. Thethree spacers 305 extend from the hub 309 at locations spacedapproximately 120 degrees around the circumference of the hub. As in theprevious embodiments, the spacers 305 have free outer ends 313 forcontacting the inner surface 41 of the burner tube 11 to position thewire holder 301 in a predetermined radial position in the burner tube bya slip fit between the wire holder and the tube.

[0034] In view of the above, it will be seen that the several objects ofthe invention are achieved and other advantageous results attained. Forexample, the portable torch 1 of the present invention with dielectricwire holder 61 has fewer parts and is easier to assemble than prior arttorches having more complicated electrically conductive wire holders.The configuration of the present invention 1 substantially fixes theposition of the spark end 33 of the igniter wire 19 in the burner tube11, thus eliminating the need for a removable threaded tip to allowaccess to the wire. The configuration of the wire holder 61 of thepresent invention also increases durability of the torch 1 by reducingthe likelihood of premature flame ignition during low-flow operation.

[0035] As various changes could be made in the above constructionswithout departing from the scope of the invention, it is intended thatall matter contained in the above description or shown in theaccompanying drawings shall be interpreted as illustrative and not in alimiting sense. For example, the wire holder 61 could be made fromceramic, thermoplastic, or other suitable dielectric materials andcomposites. The wire holder 61 could have one or more than two spacers109 regardless of the material of construction. The axial bore 83 of thewire holder 61 could have a single uniform diameter or multiple steppedsurfaces of varying diameters to secure the igniter wire 19 in theholder. The insulated igniter wire 19 may have an outer diameter equalto or smaller than the diameter of the axial bore 83 and may be securedin the wire holder 61 by means other than an interference fit with thebore (e.g., the wire may have a flattened upstream and downstreamportion deformed to have a width greater than the diameter of the axialbore to prevent the wire from being withdrawn from the wire holder). Thespacers 109 of the wire holder 61 may be arm-like members havingcircular cross-sections or other cross-sectional shapes that allow thewire holder to be fixed in the burner tube 11 while minimizing the flowdisruption of gas flowing through the tube. The wire holder 61 may bepositioned in the burner tube 11 such that the planar end surface 127 ofthe spacer 109 is the upstream end surface and the rounded end surface123 of the spacer is the downstream end surface of the wire holder.

[0036] When introducing elements of the present invention or thepreferred embodiment(s) thereof, the articles “a”, “an”, “the” and“said” are intended to mean that there are one or more of the elements.The terms “comprising”, “including” and “having” are intended to beinclusive and mean that there may be additional elements other than thelisted elements.

What is claimed is:
 1. A portable gas torch comprising a metal burnertube defining a gas flow passage through which gas is adapted to flowalong a longitudinal axis of the tube to an outlet, an igniter wire inthe gas flow passage having a spark end for generating a spark to ignitegas flowing through the passage, a wire holder for positioning theigniter wire in the gas flow passage, and a flame holder in the gas flowpassage downstream from the wire holder, said wire holder comprising acentral hub having an axial bore generally parallel to the longitudinalaxis of the burner tube and at least one spacer on the hub forcontacting an inside wall of the burner tube to position the hub at apredetermined radial location in the gas flow passage, said axial borebeing sized to enable the spark end of the wire to be inserted throughthe bore and then held at a selected location downstream from the hub,said wire holder comprising a dielectric material whereby a spark fromthe spark end of the igniter wire will jump to the inside wall of theburner tube even if the spark end is positioned closer to wire holderthan to the inside wall of the tube.
 2. A portable gas torch as setforth in claim 1 wherein said burner tube is formed from a single pieceof metal tubing from a position corresponding to the wire holder to theoutlet of the tube.
 3. A portable gas torch as set forth in claim 2wherein said burner tube has substantially uniform flow area for theflow of gas from the torch.
 4. A portable gas torch as set forth inclaim 3 wherein said burner tube is made from stainless steel.
 5. Aportable gas torch as set forth in claim 1 wherein said axial bore ofthe hub is generally coincident with the longitudinal axis of the burnertube.
 6. A portable gas torch as set forth in claim 1 wherein said axialbore of the hub is sized for gripping the wire and holding it in saidselected position.
 7. A portable gas torch as set forth in claim 6wherein said axial bore of the hub has an inlet section having a firstdiameter and a downstream section having a second diameter.
 8. Aportable gas torch as set forth in claim 7 wherein said first diameterranges from approximately 0.04 to 0.08 inches and said second diameterranges from approximately 0.02 to 0.07 inches.
 9. A portable gas torchas set forth in claim 1 wherein said at least one spacer has a roundedupstream end surface, a generally planar downstream end surface, andgenerally parallel side faces extending axially between the upstream anddownstream end surfaces.
 10. A portable gas torch as set forth in claim1 wherein said wire holder comprises a plurality of spacers extendingradially from the hub.
 11. A portable gas torch as set forth in claim 10wherein said plurality of spacers comprises a first spacer and a secondspacer located approximately 180 degrees from the first spacer.
 12. Aportable gas torch as set forth in claim 10 wherein said plurality ofspacers comprises a first spacer, a second spacer located approximately120 degrees from the first spacer, and a third spacer locatedapproximately 120 degrees from the second spacer.
 13. A portable gastorch as set forth in claim 1 wherein said wire holder dielectricmaterial comprises ceramic.
 14. A portable gas torch as set forth inclaim 1 wherein said hub and said at least one spacer are formed as asingle molded part.
 15. A portable gas torch as set forth in claim 14wherein said wire holder dielectric material comprises a thermoplasticmaterial.
 16. A portable gas torch as set forth in claim 1 wherein saidigniter wire extends beyond the wire holder a distance ranging fromapproximately 0.01 to approximately 0.08 inches.
 17. A portable gastorch as set forth in claim 16 wherein the spark end of the igniter wireis spaced in from the inside wall of the burner tube approximately 1 to6 mm.
 18. A portable gas torch as set forth in claim 1 wherein saidflame holder is spaced approximately {fraction (1/4)} inch downstreamfrom the spark end of the igniter wire.
 19. A portable gas torchcomprising a burner tube defining a gas flow passage through which gasis adapted to flow along a longitudinal axis of the tube, said tubehaving an open end defining an outlet of the torch, an igniter wire inthe gas flow passage having a spark end for generating a spark to ignitegas flowing through the passage, a dielectric wire holder in the burnertube for receiving the igniter wire and positioning the spark end in thegas flow passage, and a flame holder in the gas flow passage downstreamfrom the wire holder, said wire holder comprising a central hub havingan axial bore generally parallel to the longitudinal axis of the burnertube and a plurality of spacers extending from the hub for contacting aninside wall of the burner tube to position the hub at a predeterminedradial location in the gas flow passage. said axial bore being sized tohold said igniter wire in place by an interference fit such that thespark end of the igniter wire is held a substantially fixed distancedownstream from the hub whereby a spark from the spark end of theigniter wire will jump to the inside wall of the burner tube even if thespark end is positioned closer to wire holder than to the inside wall ofthe tube.
 20. A portable gas torch as set forth in claim 19 wherein saidplurality of spacers comprises a first spacer and a second spacerlocated approximately 180 degrees from the first spacer.
 21. A portablegas torch as set forth in claim 19 wherein said plurality of spacerscomprises a first spacer, a second spacer located approximately 120degrees from the first spacer, and a third spacer located approximately120 degrees from the second spacer.
 22. A portable gas torch as setforth in claim 19 wherein said substantially fixed distance is betweenapproximately 0.01 and approximately 0.08 inches.
 23. A portable gastorch as set forth in claim 19 wherein the spark end of the igniter wireis spaced in from the inside wall of the burner tube by approximately 1to 6 mm.
 24. A portable gas torch as set forth in claim 19 wherein saidwire holder dielectric material comprises ceramic.
 25. A portable gastorch as set forth in claim 19 wherein said hub and said at least onespacer are formed as a single molded part.
 26. A portable gas torch asset forth in claim 25 wherein said wire holder dielectric materialcomprises a thermoplastic material.